{
 "cells": [
  {
   "cell_type": "markdown",
   "id": "5457cd07",
   "metadata": {},
   "source": [
    "### 函数\n",
    "\n",
    "* [函数的定义](https://docs.python.org/3/tutorial/controlflow.html#defining-functions)\n",
    "   * 数学 ： f(x) = ax + b\n",
    "   * python ： def fib(x):\n",
    "   * 编程思维 VS 数学思维\n",
    "      * 函数可以被定义名称,定义的关键字 def\n",
    "      * 数学思维是写在同一行（定义函数 和 运算公式）, 面向对象编程中 函数写多行，定义函数为单独一行\n",
    "       * 数学函数一般没有注释，而编程过程中，一般需要对函数进行注释描述（docstring，课本P151）\n",
    "       * 数学中：ax + b 是计算公式 ，而编程中，我们将函数的内容成为函数体,函数体要有一定的缩进\n",
    "       * 数学函数执行，将参数带入公式 ， 编程中函数执行，将参数带入函数体\n",
    " \n",
    " \n",
    "* [ 关于函数的更多定义](https://docs.python.org/3/tutorial/controlflow.html#more-on-defining-functions)\n",
    "  * 函数的参数\n",
    "      * 形式参数\n",
    "      * 实际参数\n",
    "      * 默认参数\n",
    "      * 位置参数\n",
    "      * 关键字参数"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "958d168e",
   "metadata": {},
   "source": [
    " #### 函数的定义\n",
    " * 定义函数\n",
    " \n",
    " ```\n",
    " def:定义函数的关键字\n",
    "flb：函数名\n",
    "(n)：定义函数的参数\n",
    "\"\"\"  \"\"\"：文档描述 : 与使用者进行 交互的唯一途径\n",
    "代码块：\n",
    "     a, b = 0, 1\n",
    "     while a < n:\n",
    "        print(a, end=' ')\n",
    "         a, b = b, a+b\n",
    "     print()\n",
    "````"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "id": "821d06b7",
   "metadata": {},
   "outputs": [],
   "source": [
    "# 斐波那切数列： 0 1 1 2 3 5 8 13 21 34 ...\n",
    "def fib(x):\n",
    "    \"\"\"列出指定x以内的斐波那切数列\"\"\"\n",
    "    a,b = 0,1\n",
    "    while a < x :\n",
    "        print(a,end=\" \")\n",
    "        a,b = b, a+b "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "id": "6f8c34b9",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "0 1 1 2 3 5 8 13 21 34 55 89 "
     ]
    }
   ],
   "source": [
    "fib(100)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "id": "caa8625a",
   "metadata": {},
   "outputs": [],
   "source": [
    "# 实践： 请大家写一个函数，这个函数可以打印 “你好，XXX同学~”\n",
    "def hello(name):\n",
    "    \"\"\"显示问候语\"\"\"\n",
    "    print(\"你好，%s同学~\"%(name))"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "ab8776c9",
   "metadata": {},
   "source": [
    "* 调用函数/使用函数\n",
    "  * 函数名(参数)\n",
    "  * 参数可以不存在"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "id": "1b83f4f3",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "你好，Lihua同学~\n"
     ]
    }
   ],
   "source": [
    "hello(\"Lihua\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "id": "d08bc3c9",
   "metadata": {},
   "outputs": [],
   "source": [
    "def hello():\n",
    "    \"\"\"显示问候语\"\"\"\n",
    "    print(\"hello,world\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "id": "1363a699",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Help on function hello in module __main__:\n",
      "\n",
      "hello()\n",
      "    显示问候语\n",
      "\n"
     ]
    }
   ],
   "source": [
    "help(hello)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "id": "c406a05a",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "hello,world\n"
     ]
    }
   ],
   "source": [
    "hello()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "id": "ecb061ba",
   "metadata": {},
   "outputs": [],
   "source": [
    "# 回顾与思考\n",
    "import time"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "id": "8277255b",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "time.struct_time(tm_year=2022, tm_mon=1, tm_mday=7, tm_hour=4, tm_min=22, tm_sec=30, tm_wday=4, tm_yday=7, tm_isdst=0)"
      ]
     },
     "execution_count": 9,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# localtime() 不需要给定参数\n",
    "time.localtime()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "id": "ade04ba6",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Help on built-in function localtime in module time:\n",
      "\n",
      "localtime(...)\n",
      "    localtime([seconds]) -> (tm_year,tm_mon,tm_mday,tm_hour,tm_min,\n",
      "                              tm_sec,tm_wday,tm_yday,tm_isdst)\n",
      "    \n",
      "    Convert seconds since the Epoch to a time tuple expressing local time.\n",
      "    When 'seconds' is not passed in, convert the current time instead.\n",
      "\n"
     ]
    }
   ],
   "source": [
    "help(time.localtime)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "e7a9d72c",
   "metadata": {},
   "source": [
    "* 函数的优势\n",
    "  * 可以重复使用相同的功能，避免重复造轮子\n",
    "  * 使用者可以不了解函数本身，只需要清楚如何使用即可\n",
    "  * 使用/调用方便，只需要清楚传递的 函数名及参数\n",
    " "
   ]
  },
  {
   "cell_type": "markdown",
   "id": "1165ebca",
   "metadata": {},
   "source": [
    "#### 函数的参数\n",
    "* 形式参数（形参））：形式参数，不是实际存在的，是虚拟变量。在定义函数和函数体的时候使用形参，目的是在函数调用时接收实参\n",
    "   * 在定义函数的时候定义的参数\n",
    "   * 形式参数不占用内存\n",
    "\n",
    "* 实际参数（实参）：实际参数，调用函数时传递给函数的参数，可以是常量、变量，表达式，函数，传给形参\n",
    "  * 在调用函数的时候传递的参数\n",
    "  * 调用函数时，形式参数分配空间，传递实际参数，执行函数内容\n",
    "  \n",
    "* 课本函数实践案例：\n",
    "```\n",
    "def search4vowels(word):\n",
    "    \"\"\"显示文本中出现的元音字母有哪些\"\"\"\n",
    "    vowels = set(\"aeiou\")\n",
    "    word = set(word)\n",
    "    print(vowels & word)\n",
    "    \n",
    "    # 形式参数： word\n",
    "    # 实际参数：\"fbheduigpewjiewmcfkdlaepw\"\n",
    "    ```\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "id": "6e813d2a",
   "metadata": {},
   "outputs": [],
   "source": [
    "#  课本函数实践案例\n",
    "def search4vowels(word):\n",
    "    \"\"\"\n",
    "    显示文本中出现的元音字母有哪些\n",
    "    \n",
    "    word是文本信息，请输入正确的文本给word\n",
    "    \"\"\"\n",
    "    vowels = set(\"aeiou\")\n",
    "    word = set(word)\n",
    "    print(vowels & word)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "id": "f4719304",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Help on function search4vowels in module __main__:\n",
      "\n",
      "search4vowels(word)\n",
      "    显示文本中出现的元音字母有哪些\n",
      "    \n",
      "    word是文本信息，请输入正确的文本给word\n",
      "\n"
     ]
    }
   ],
   "source": [
    "help(search4vowels)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "id": "77ffb0bb",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{'a', 'u', 'i', 'e'}\n"
     ]
    }
   ],
   "source": [
    "search4vowels(\"fbheduigpewjiewmcfkdlaepw\")"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "639deb2b",
   "metadata": {},
   "source": [
    "* 在多个参数的情境下\n",
    "  * 位置参数(positional argument)\n",
    "     * 在形式参数的定义中，有一定的先后顺序\n",
    "     * 在调用函数时，要考虑形参的先后顺序\n",
    "     * 调用函数时，不仅要考虑参数位置，还需要考虑形式参数的个数\n",
    "     \n",
    "  * 关键字参数 \n",
    "     * 在调用函数时，关键字参数可以不考虑形式参数的位置\n",
    "     \n",
    "  * 默认参数\n",
    "     * 调用函数时，可以省略传递的参数信息\n",
    "     * 调用函数时，如果给默认参数赋值，会替换默认参数的结果"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "id": "76b322dc",
   "metadata": {},
   "outputs": [],
   "source": [
    "def describe_pet(pet_name,animal_type):\n",
    "    \"\"\"显示宠物信息\"\"\"\n",
    "    print(\"\\nI have a \" + animal_type + \".\")\n",
    "    print(\"My \" + animal_type + \"'s name is \"+pet_name.title() + \".\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "id": "334a6fa2",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "\n",
      "I have a dog.\n",
      "My dog's name is 豆豆.\n"
     ]
    }
   ],
   "source": [
    "describe_pet(\"豆豆\",\"dog\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "id": "b0d8fa4e",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "\n",
      "I have a 豆豆.\n",
      "My 豆豆's name is Dog.\n"
     ]
    }
   ],
   "source": [
    "describe_pet(\"dog\",\"豆豆\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "id": "800bf429",
   "metadata": {},
   "outputs": [
    {
     "ename": "TypeError",
     "evalue": "describe_pet() missing 1 required positional argument: 'animal_type'",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-17-7b9959e7e395>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[0mdescribe_pet\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m\"豆豆\"\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mTypeError\u001b[0m: describe_pet() missing 1 required positional argument: 'animal_type'"
     ]
    }
   ],
   "source": [
    "describe_pet(\"豆豆\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "id": "da0560fa",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "\n",
      "I have a cat.\n",
      "My cat's name is 微积分.\n"
     ]
    }
   ],
   "source": [
    "describe_pet(animal_type=\"cat\",pet_name=\"微积分\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "id": "7055a5b3",
   "metadata": {},
   "outputs": [],
   "source": [
    "## 默认参数\n",
    "def describe_pet(pet_name,animal_type=\"dog\"):\n",
    "    \"\"\"显示宠物信息\"\"\"\n",
    "    print(\"\\nI have a \" + animal_type + \".\")\n",
    "    print(\"My \" + animal_type + \"'s name is \"+pet_name.title() + \".\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "id": "06b86b34",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "\n",
      "I have a cat.\n",
      "My cat's name is 豆豆.\n"
     ]
    }
   ],
   "source": [
    "describe_pet(\"豆豆\",\"cat\")"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "ee18504c",
   "metadata": {},
   "source": [
    "* 参数注意事项实践\n",
    "  * 位置参数和关键字参数同时使用（调用函数）\n",
    "     * positional argument follows keyword argument（关键字参数均应该放在位置参数之后）\n",
    "     * 只要满足1的条件，剩余的关键字参数（多个）不考虑先后顺序\n",
    "     \n",
    "  * 非默认参数和默认参数同时使用（定义函数）\n",
    "     * non-default argument follows default argument（默认参数均应该放在非默认参数之后）\n",
    "     * 只要满足1的条件，剩余的默认参数（多个）不考虑先后顺序"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 21,
   "id": "a96dc4fd",
   "metadata": {},
   "outputs": [],
   "source": [
    "def test(x,y,z):\n",
    "    \"\"\"打印x,y,z的结果\"\"\"\n",
    "    print(x)\n",
    "    print(y)\n",
    "    print(z)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "id": "41d67c6a",
   "metadata": {},
   "outputs": [
    {
     "ename": "SyntaxError",
     "evalue": "positional argument follows keyword argument (<ipython-input-22-489fdb94d38c>, line 2)",
     "output_type": "error",
     "traceback": [
      "\u001b[1;36m  File \u001b[1;32m\"<ipython-input-22-489fdb94d38c>\"\u001b[1;36m, line \u001b[1;32m2\u001b[0m\n\u001b[1;33m    test(5,y=3,2)\u001b[0m\n\u001b[1;37m               ^\u001b[0m\n\u001b[1;31mSyntaxError\u001b[0m\u001b[1;31m:\u001b[0m positional argument follows keyword argument\n"
     ]
    }
   ],
   "source": [
    "# 实践1：\n",
    "test(5,y=3,2)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 23,
   "id": "bf8eb7c2",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "5\n",
      "3\n",
      "2\n"
     ]
    }
   ],
   "source": [
    "# 实践2：\n",
    "test(5,3,z = 2)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 24,
   "id": "ace588d5",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "5\n",
      "2\n",
      "3\n"
     ]
    }
   ],
   "source": [
    "# 实践3：\n",
    "test(5,z=3,y=2)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 25,
   "id": "36e78cdb",
   "metadata": {},
   "outputs": [
    {
     "ename": "SyntaxError",
     "evalue": "non-default argument follows default argument (<ipython-input-25-eac1f1ed18cb>, line 2)",
     "output_type": "error",
     "traceback": [
      "\u001b[1;36m  File \u001b[1;32m\"<ipython-input-25-eac1f1ed18cb>\"\u001b[1;36m, line \u001b[1;32m2\u001b[0m\n\u001b[1;33m    def test(x,y=1,z):\u001b[0m\n\u001b[1;37m             ^\u001b[0m\n\u001b[1;31mSyntaxError\u001b[0m\u001b[1;31m:\u001b[0m non-default argument follows default argument\n"
     ]
    }
   ],
   "source": [
    "# 测试2：\n",
    "def test(x,y=1,z):\n",
    "    \"\"\"打印x,y,z的结果\"\"\"\n",
    "    print(x)\n",
    "    print(y)\n",
    "    print(z)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 26,
   "id": "dfd3a29e",
   "metadata": {},
   "outputs": [],
   "source": [
    "def test(x,z,y=1):\n",
    "    \"\"\"打印x,y,z的结果\"\"\"\n",
    "    print(x)\n",
    "    print(y)\n",
    "    print(z)"
   ]
  }
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